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Written by David Ramsey   
Monday, 14 February 2011
Table of Contents: Page Index
Xigmatek Achilles Plus SD1484 Heatsink
Closer Look: Achilles Plus Prototype
Heatsink Test Methodology
Testing and Results
CPU Cooler Final Thoughts and Conclusion

Heatsink Test Methodology

Benchmark Reviews is obsessed with testing CPU coolers, as our Cooling Section has demonstrated over the past few years. We've solicited suggestions from the enthusiast community, and received guidance from some of the most technical overclockers on the planet. As a result, our testing methodology has changed with every new edition of our Best CPU Cooler Performance series. Because of this, each article is really its own stand-alone product, and cannot be fairly compared to the others. Benchmark Reviews continues to test CPU coolers using the stock included fan (whenever applicable), and then replace it with a high-output fan for re-testing.

Manufacturers are not expected to enjoy this sort of comparison, since we level the playing field for all heat sinks by replacing their included fan with a common unit which is then used for every CPU cooler tested. Many manufacturers include fans with their heat sink products, but many 'stock' fans are high-RPM units that offer great airflow at the expense of obnoxiously loud noise levels, or, conversely, quiet fans that sacrifice performance for low noise. By using the same model of cooling fan throughout our heat sink tests, we can assure our results are comparable across the board. This is one of the more significant changes we have made to our test methodology, since many of the benchmark tests we have conducted in the past have compared the total package. Ultimately we're more interested in the discovering the best possible heat sink, and we believe that you'll feel the same way.

For each test, ambient room temperature levels were maintained within one degree of fluctuation, and measured at static points beside the test equipment with a digital thermometer. The Corsair H70 and the comparison coolers used a common Thermal Interface Material of our choosing (listed in the support equipment section below) for consistency. The processor received the same amount of thermal paste in every test, which covered the heat spreader with a thin nearly-transparent layer. The heat sink being tested was then laid down flat onto the CPU, and compressed to the motherboard using the supplied retaining mechanism. If the mounting mechanism used only two points of force, they were tightened in alternation; standard clip-style mounting with four securing points were compressed using the cross-over method. Once installed, the system was tested for a baseline reading prior to testing.

At the start of each test, the ambient room temperature was measured to track any fluctuation throughout the testing period. AIDA64 Extreme Edition is utilized to create 100% CPU-core loads and measure each individual processor core temperature. It's important to note that software-based temperature reading reflects the thermal output as reported from the CPU to the BIOS. For this reason, it is critically important (for us) to use the exact same software and BIOS versions throughout the entire test cycle, or the results will be incomparable. All of the units compared in our results were tested on the same motherboard using the same BIOS and software, with only the CPU-cooler product changing in each test. These readings are neither absolute nor calibrated, since every BIOS is programmed differently. Nevertheless, all results are still comparable and relative to each products in our test bed (see The Accuracy Myth section below).

Since our test processor reports core temperatures as a whole number and not in fractions, all test results utilize ADIA64 to report averages (within the statistics panel), which gives us more precise readings. The ambient room temperature levels were all recorded and accurate to one-tenth of a degree Celsius at the time of data collection.

When each cooler is tested, Benchmark Reviews makes certain to keep the hardware settings identical across the test platform. This enables us to clearly compare the performance of each product under identical conditions. Benchmark Reviews reports the thermal difference; for the purposes of this article, thermal difference (not the same as thermal delta) is calculated by subtracting the ambient room temperature from the recorded CPU temperature.

Please keep in mind that that these test results are only valid within the context of this particular test: as the saying goes, your mileage may vary.

Intel Test System

  • Processor: Intel Core i7-950 Bloomfield 3.06GHz LGA1366 130W Quad-Core Processor Model BX80601950, core voltage set to 1.35V
  • Motherboard: ASUS Sabertooth X58 Intel X58-Express chipset) with BIOS 0603, BCLK set to 175MHz for a processor speed of 4025MHz

Support Equipment

  • AIDA64 Extreme Edition version 1.50.1200
  • MG Chemicals Heat Transfer Compound 8610-60G
  • Stock fan (for heat sinks without fans): Thermalright TR-FDB-12-1600 (63.7CFM advertised)
  • High-speed fan: Delta AFC1212D (113CFM advertised)

All of the tests in this article have been conducted using vertical motherboard orientation, positioned upright in a traditional tower computer case. Air-cooled heat sinks are positioned so that heatpipe rods span horizontally, with the fan blowing air out the top of the chassis. The radiators of water coolers are mounted as per manufacturer instructions. In both cases, fans are connected directly to the power supply (rather than motherboard headers) and run at full speed during the test. At the start of our test period, the test system is powered on and AIDA64 system stability tests are started with Stress CPU and Stress FPU options selected. AIDA64 loads each CPU core to 100% usage, which drives the temperature to its highest point. Finally, once temperatures have sustained a plateau (no observed change in average temperatures for 5 minutes), the ending ambient room temperature and individual CPU core levels are recorded thus completing the first benchmark segment. The time to reach stable temperatures varied between 10 and 20 minutes for the heat sinks in this test; larger heat sinks typically take longer to stabilize.

The second test segment involves removing the stock cooling fan and replacing it with a high-output 120 mm Delta AFC1212D cooling fan, then running the same tests again.

Note: Both the Antec KühlerH2O 620 and the CoolIt Vantage A.L.C. are designed to drive their own RPM-controlled fans directly; in the case of the Vantage, an alarm will sound continuously if there is no fan connected. For these coolers, the fans were left connected as designed during stock fan testing. For high-speed fan testing, the Delta fan was connected directly to the power supply (and the alarm on the Vantage ignored).

The Accuracy Myth

All modern processors incorporate an internal thermal diode that can be read by the motherboards' BIOS. While this diode and the motherboard are not calibrated and therefore may not display the actual true temperature, the degree of accuracy is constant. This means that if the diode reports 40°C when it's actually 43°C, then it will also report 60°C when it's truly 63°C. Since the design goal of any thermal solution is to keep the CPU core within allowable temperatures, a processor's internal diode is the most valid means of comparison between different heat sinks, or thermal compounds. The diode and motherboard may be incorrect by a small margin in relation to an actual calibrated temperature sensor, but they will be consistent in their margin of error every time.



# Faulty assumption.Olle P 2011-02-15 07:49
Two fans mounted in series will *not* move twice as much air as a single fan. (In free air they will move just a little more than a single fan.)
They will, however, be the equivalent of a *stronger* fan, able to build a higher pressure. That is good if the air flow is very constricted by dense fins or so, like in the case of the H70 cooler. It's a very noisy solution though.
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# RE: Xigmatek Achilles Plus SD1484 HeatsinkDavid Ramsey 2011-02-15 08:50
Let's try a though experiment: take two 90CFM fans as used on the V6 GT. Put them in series-- the output of one blowing towards the input of another-- but space the fans 6 feet apart. In this configuration the aggregate air flow of the fans is obviously 180CFM, although it's really two independent air streams.

The question is "How close do the fans have to be before the aggregate air flow drops?" A secondary question would be "How does the introduction of an obstruction affect this?"

Obviously a 90CFM fan isn't going to blow 90CFM through the tightly-packed fins of a typical cooler, but I don't know of a good way to measure this. Custom PC magazine did a fan test roundup some years back where they measured how long a given fan took to inflate a garbage bag of known volume, and that might be worth trying.
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# RE: RE: Xigmatek Achilles Plus SD1484 HeatsinkServando Silva 2011-02-15 09:20
Time to get a digital anemometer and test it. It sounds like a very interesting experiment.
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# RE: RE: RE: Xigmatek Achilles Plus SD1484 HeatsinkDavid Ramsey 2011-02-15 12:43
Yeah, well, the trouble with that is that commercial anemometers are designed to test air flow in HVAC systems, and generally have low-end CFM ranges of about 80CFM, which means they wouldn't be able to give readings on the majority of fans...
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# RE: RE: RE: RE: Xigmatek Achilles Plus SD1484 HeatsinkServando Silva 2011-02-15 13:03
Majority of the fans? I'd say most of the enthusiasts use fans below the 80CFM Spec. Fans included with heat-sinks or radiators normally stay between 30-80CFM range. Only when you're looking for an specific test or if you're overclocking a lot your components you'll go for a delta or any other 80+ CFM fan, because they sound like vacuums.

Also, for measuring performance, readings should be measured after passing the radiator/heatsink. So even if a 80CFM fan is mounted, I doubt you'll see 80 CFM after passing trough the heatsink, and will also depend a lot on static pressure for sure.

Anyway, I think there are a lot of fans to test in those conditions. The only problem I can think off, is that we should tap or make a tunnel after the heatsink/rad to make proper measurements, I suppose. Here's a simple, yet useful example at Xtreme Systems:
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# RE: RE: RE: RE: RE: Xigmatek Achilles Plus SD1484 HeatsinkDavid Ramsey 2011-02-15 13:16
Um, yeah. Isn't "majority" similar in meaning to "most of"?

If we're measuring a fan's output to see how well it corresponds to its advertised rating, we'd need to measure the fan in isolation. The performance with specific heat sinks might be interesting, but in that case we'd be testing the heat sink more than the fan...

The video was interesting, but with no explanation of what was being measured or how it was being measured, I didn't get any useful information from it. I assume the orange meter at the right was showing volts, and perhaps one of the three devices to the left was reading out CFM, but I don't really know.
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# RE: RE: RE: RE: RE: RE: Xigmatek Achilles Plus SD1484 HeatsinkServando Silva 2011-02-15 13:29
Yes, but really, most of the PC fans work above 80CFM?
Oh, It's my fault not to include a link to the specific thread. From left to right: anemometer, sound meter 1, sound meter 2 (on a cellphone, which I don't trust), Fan Voltage. I thought the video was clear enough to see the units, but maybe because I saw it at 1080p res.
I think we'd be testing both heatsink/radiator performance and fan performance.
Here's the link for complete info at XS:

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# RE: RE: RE: RE: RE: RE: RE: Xigmatek Achilles Plus SD1484 HeatsinkDavid Ramsey 2011-02-15 13:40
It would be nice to know which anemometer he was using, since it can obviously handle low air flows...
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# RE: RE: RE: RE: RE: RE: RE: RE: Xigmatek Achilles Plus SD1484 HeatsinkServando Silva 2011-02-15 13:51
OK, now that I've re-read your phrase I need to apologize because I misread it. You actually meant low-end CFM ranges about 80 CFM, and I understood it the other way. Now all makes sense.

About the model, I could easily read it while watching the video. It's an AM-4836V. Google lead me here:
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# RE: RE: RE: RE: RE: RE: RE: RE: RE: Xigmatek Achilles Plus SD1484 HeatsinkDavid Ramsey 2011-02-15 13:58
There doesn't seem to be any way to get one except to order it directly from China, and the price is unknown (all the dozens of web pages just say "Contact" or "Quote", apparently because they want to sell you bulk quantities), but now that I know these low-air-flow anemometers exist, I'll see if I can find one.
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# RE: RE: RE: RE: RE: RE: RE: RE: RE: RE: Xigmatek Achilles Plus SD1484 HeatsinkServando Silva 2011-02-15 14:10
There are other models supporting 0-9999 CFM like this:

Ebay could also be an option.
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# Not that hard...Olle P 2011-02-17 03:48
"How close do the fans have to be before the aggregate air flow drops?"
Assuming the fans are placed freely the answer is very simple to detect experimentally: Move them slowly closer until they start to increase their rotational speed. That's when the interaction between them is big enough to notice. (I've done this myself, and the distance do differ with the force and geometry of the fans.)
When mounted at the opposite sides of a heatsink one can easily assume a negligible amount of air to not pass through both fans. Especially if the heatsink, like in the V6, is a closed tunnel.

"How does the introduction of an obstruction affect this?"
It does reduce the airflow, in the case of high speed fans the reduction is substantial, as can be read from the pressure/flow curves supplied by the fan manufacturers.
The typical optimal work-span for most fans is at around half of the free flow, and then it's up to the user to pick a fan that have a span covering the desired flow and pressure applicable.
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# Xigmatek Achilles Plus SD1484 prototypeDavid Ramsey 2011-02-15 14:17
Servando, the anemometer at the link you supplied (the CEM DT-619) specifically says that the lower bound it supports is 80CFM...
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# RE: Xigmatek Achilles Plus SD1484 prototypeServando Silva 2011-02-15 17:11
I'm sorry David but I fail to see that in the specifications table. It says it supports a minimum of 0 CFM and a maximum of 9999CFM. However I do see that it supports a minimum of 80 ft/min, which stands for speed, not volume (air-flow).
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# RE: RE: Xigmatek Achilles Plus SD1484 prototypeDavid Ramsey 2011-02-15 17:16
You're right, my bad. I suppose to use this for fan testing, I'd have to construct some sort of tunnel so that all the air flow from the fan was focussed through the blades of the anemometer...
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